1. Field of the Invention
The present invention relates to a damper plate and a method for producing the damper plate, and more particularly to a damper plate used in a gap between an impeller and a casing, as a thrust pad or a radial pad of a slide shaft bearing, or at a sealing surface of a floating seal device in a rotary machine such as a pump.
2. Description of the Related Art
A damper plate is used in a rotary machine to reduce the amount of fluid leakage between a rotating body and a stationary portion so as to increase efficiency of the rotary machine and provide a cushioning or bearing effect to decrease deflection of the rotating body. Thus, the damper plate is required to be tough enough to withstand a contact with the rotating body which rotates at a high speed. The damper plate is also required to have accurate polygon patterns which perform the cushioning effect in response to the deflection of the rotating body. Also, the damper plate is preferred to be formed in a thin plate so that it can easily bend to fit a curved surface for easy mounting.
One of the examples of such a damper plate is a honeycomb plate shown in FIGS. 6A through 6D, having a plurality of convexoconcaves of a hexagonal cross-section. Conventionally, the honeycomb plate is produced by one of the following methods:
(1) Machine processing using a three-dimensional processing machine PA1 (2) Etching process using a thin film mask having a plurality of polygonally patterned holes attached on the metal plate PA1 (3) Laser beam processing using the energy of a laser beam PA1 (4) Blasting method using a mask
Since it is difficult to shape convexoconcaves by one step with this method, the plate is first processed to have holes and then incorporated with a bottom plate by brazing or other adhering methods.
A thin film mask has a plurality of polygonal holes and is secured to the metal plate, in the same way as the etching method. Blasting particles are ejected to define convexoconcaves thereon.
However, each of these methods has the following disadvantages:
(1) Machine Processing
Since fine processing is required, a tool used in the processing is easily worn out and a processing time is long.
(2) Etching Method
Since a periphery of the hole is also etched through the process, the accurate polygonal patterns cannot be achieved. Also, in order to perform a uniform etching, the selection of material is limited.
(3) Laser Beam Machining
A number of steps are required and the cost is expensive.
(4) Blasting Method
Since the thin film mask is also exhausted by the blasting, the processing can be performed only while the thin film remains, and thus deep concaves are difficult to be defined. Also, since a hard or tough material cannot be processed, the materials useable in the process are limited.
For the foregoing reasons, there is required to provide a practical method for producing a honeycomb-type damper plate with a high dimensional accuracy and reasonable cost. Particularly, when a dimensional accuracy is not established, the gap between the damper plate and the rotating body needs to be larger to prevent contacts or galling therebetween. In this case, the rotary machine having a high performance and less vibration cannot be provided by employing the advantages of the honeycomb plate.